Apparatus for plating finely divided material



2 Sheets-Sheet 2 W. W. CASTOR APPARATUS FOR PLATING F'INELY DIVIDEDMATERIAL Filed Nov. 4, 1941 April 16, 1946.

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,4 l A A Patented Apr. 1c, 1946 UNITED STATES PATENT OFFICE Wilbur W.Castor, Mount Lebanon, Pa.

Application November 4,1941, Serial No. 417,866

1 Claim. (Cl. ill-12.2)

This invention relates to metal plating, and specifically to apparatusforplating by condensation of metal from vaporous to solid state. Theobject in view is primarily the production of plated articles of minutesize, articles that in this respect are of'very dlflerent character fromarticles that have-in such manner been plated heretofore, and articlesdesigned for and adapted to other specific uses, as will hereinafter beenumerated.

In the accompanying drawings Fig. I is a' view.

in vertical section of apparatus ofthe invention, with accessoryinstrumentalities shown diagrammatically; Fig. 11 is a view to smallerscale, showing in side elevation the apparatus of Fig. I; and Fig. Illis a view corresponding to Fig. I, that shows the apparatus in modifiedform.

In a companion application I have described and claimed a metal-platedparticle-typically, a particle of mica plated with aluminum--adapted tobe used, in substitution for a homogeneous particle of aluminum, in thepreparation. of aluminum paint. I now show the apparatus in which andthe method by which the plating of such an article is effected.

In Fig. I of the drawings a vacuum chamber l is shown. Its walls mayconveniently be formed of steel. A vacuum pump 2 is connected with thechamber, for the purpose of exhausting the air and creating within thechamber an ap roxithat the illustration ofthe pump is conventionalmerely. I have in fact employed an oil pump and a mechanical pumpoperating together, and

I have done this both to speed up the evacuating them the leads 8 of anelectric circuit may be connected. The chamber contains a dredge 4 and areceptacle 6, so shaped and arranged that from the dredge 4. finelydivided material disseminated by the shaking of the dredge may be causedto fall-to be rained down as a curtain M throughout substantially theentire vertical extent of the chamber. The ialling curtain of materialpasses near the centrally arranged fila- -mately perfect vacuum. It-maybe understood ment 3. The dredge is so mounted that it may be shaken. Ashere shown it is pivoted upon a horizontally extending axle 9. A springI0 is provided, under whose tension the dredge is normally held at oneend' of a suitable range of oscillation. To such limit the oscillatingdredge is held by the abutment of a dredge-borne finger I l upon a stopl2. The finger ll serves also as the armature of an electro-magnet 5,and in response to intermittent energizing of the magnet thespring-backed dredge oscillates between positions in-which the finger llabuts upon stop l2 and upon the core I'3 of the, electro-magnet.

The chamber is advantageously equipped with a thermocouple it; it may beequipped with a vacuum gauge as well; and it will be understood that thecurrent that is caused to flow through the filament 3 may be subject toobservation (that its character may be properly adjusted) by means of anammeter and a volt meter. Suitable means (not shown) may also beprovided for cooling the chamber and its contents.

The chamber wall on one side I5 is removable. that access may be had forthe charging and removal of materials and for the maintenance ofoperative conditions.

In typical operation the chamber is opened and two hairpin bends ofaluminum wire A are hung on the coil 3. The aluminum wire may be 0.032of an inch in diameter and the two pieces may be each half an inch long.A charge of mica particles is placed in the dredge 4. The particles ofthis charge may be of the order of 0.5- 5.0 microns in thickness. Thequantity may be a tenth of a gram and upward. The chamber then is closedand is evacuated to a pressure of 25 microns. A current of amperes at atension of 5 volts is caused to flow in the circuit that includes thefilament 3, and under the heat generated by such flow the aluminum ofthe two lengths of wire is initially melted and flows as a coating uponthe tungsten filament. The flow of current is continued; and, undercontinued heat, the aluminum coating upon the tungsten filament isvaporized and the vapor fills the evacuated chamber. The dredge A thenis agitated and the mica particles are rained down in the form of acurtain M through the vapor. Upon the descend ing particles the vaporcondenses and forms a fine plating over all of the surfaces of all of'the particles. The so plated particles fall into the receptacle 6; and,when the descent of the particles is completed, the flow of currentthrough the tungsten filament, and the fiow of the current that effectsoscillation of the dredge as well, are

cut off; the vacuum within the chamber is. relieved; cooling is resortedto; the chamber is opened; and the plated particles are removed from thereceptacle 8.

The particles will be found to be plated with a continuous andall-covering plating of aluminum of a thickness of the order of three tofive millionths of an inch, and a film of lustrous appearance. Suchparticles, when they have been subjected to an operation of filming overwith stearic acid, may advantageously be applied in place of all-metalflakes of aluminum, in the preparation ofpaints, lacquers, etc., as isexplained in the companion application, alluded to above.

It is manifest that the aluminum vapor when it has been caused to fillthe chamber I will condense, not on the falling particles of mica only,but upon all surfaces with which it comes into contact. In continuedoperation of the apparatus, therefore, the inner surfaces of the chamberwalls and the surfaces of dredge 4 and receptacle 6 will from time totime be scraped to recover condensed aluminum. This, however, isfamiliar practicein the use of apparatus frcoating in like manner thesurfaces of mirrors.

The color of the plating upon the particles may. be modified byincluding within the chamber small quantities of specific substances.For example, a small amount of paraffin oil will give to the plating apurplish cast; the inclusion of wool fibre will produce an amber tingedplating, etc. Excessive and prolonged temperature maintained in thetungsten filament will result in a yellowing of the deposit. Inevitablythere will be some small wastage of thetungsten filament; normally thisis so slight as to have no appreciable modifying effect upon the platedparticles so far as concerns their intended uses; and, manifestly, inthe interest of economy, conditions of an operation (and, particularly,time and temperature) will be so controlled and limited that, while thedesired end is gained, the tungsten is not unnecessarily spent.

In the apparatus in modified form and as shown in Fig. 111, the chamber2| is cylindrical and stands vertically; and it is provided with aremovable upper head 22. The aluminum to be vaporized and condensed isinitially carried in a small crucible. 23 of suitable material and thecrucible in the assembly is so mounted that its contents come within.the electro-magnetic field of a coil 25. The coil is such and theenergizing current, voltage, and frequency are such as to vaporize thecharge of aluminum within the crucible. The crucible is arrangedcoaxially with and in the lower part of the chamber. The dredge 24 andthe receptacle 28 are in this case of annular form, and the curtainthatis rained down is in the form of a cylindrical shell, surroundingthe cloud of vapor that rising from the crucible spreads and fills thechamber. By way of illustrating alternative means of agitating thedredge, the dredge hereis shown to be linked to and suspended fromspindles 29, and to be articulated to the armature 26 of an A. C.solenoid 21. It is manifest that the vibratory movement of the armatureis imparted directly and immediately to the dredge.

Procedure is essentially such as has already been detailed. when, by themaintenance of an electro-magnetic field of suilicient intensity thecharge of aluminum passes to vaporous condition, rising as a cloud fromthe crucible and' tated; the particles. of mica are rained down throughthe vapor; and aluminum condenses upon them as they fall.

I have described the plating of mica. with aluminum as typicalprocedure. The invention in its broader aspect contemplates the platingof powdered material generally with metal generally, and presently Ishall indicate the wide and diverse fields. of utility that may beserved in the practice of my invention. Among materials to be plated, Icontemplate flake-like particles of mica and of graphite; amorphous andporous particles, such as particles of carbon, dense and crystallineparticles, such as those of silica; and particles of metal, ordinarilybase metal such as iron and copper, tobe plated with precious metal,such as silver and gold. Procedure with the apparatus of Fig. I issubject to this limitation, that the vaporized metal must have a pointof vaporization in vacuo definitely lower than the melting point oftungsten; but the apparatus of Fig. 11

is attended by -no such limitation in use. Metals The utility oftheinvention in widely varied fields may be indicated. In the field ofpaints and lacquers, a quantity of aluminum-plated flakes of mica, or ofgold-plated grains of silica for a given coverage is cheaper than a likequantity of homogeneous metallic particles, and may be provided at lesstotal cost; the plated material is of less specific gravity, and inconsequence is better suited to the conditions of use; the platedparticles may be produced in quantity and of better uniformity in sizethan is possiblein the production of homogeneous metal particles, and onthat account also the plated material is better adapted to the use andwill afford better coverage.

In the allied art of the decoration of ceramic ware the plated powdermay be used to advantage, in place of homogeneous metallic powder; andin the art of printing the plated powder may advantageously be used inplace of homogeneous metal powder in the preparation of printing inks(using ink in an extended sense, to include liquid and plasticpreparations that are printed as ink is printed) In the art of powdermolding, plated powder is equally responsive with homogeneous metalpowder to the molding operation, and may be employed with the advantageof cheapness, and, where weight is disadvantageous, with the advantageof lightness. The carrier particles may be either inert and rigid orthey may be of mateand integrating a mass of such particles.

In the manufacture of abrasive instruments, particles of abrasive mayinitially be plated with metal that they may be the more securely heldin the body of metal that constitutes the matrix in which they are inthe course of manufacture included.

In the practice of the invention particles of spreading within thechamber, the dredge is agi- 76 a given metal may by plating with anothermetal v intimately mingled but unalloyed becomes possible by plating ofparticles of one metal with another be protected from oxidation, and sothe alloying of the two metals involved may be facilitated.

The plated coating may be relied upon, not only to prevent particularfinely divided material from oxidation, but also to isolate it, so thatit will not 6 injuriously react with other materials with which 'forother reasons it is desirably brought into contact.

A catalytic sponge may be prepared by plating desired metal orcompound-with nickel, for example.

- vapor. porous particles of copper, for example, with the 10 WILBUR W.CASTOR.

